1. Field of the Invention
The invention relates to electronic surveillance (ES) and electronic counter measure (ECM) systems and, in particular, to a portable device capable of passively collecting and storing all digitized radio frequency (RF) pulse data received by an electronic surveillance system. The invention further relates to the method by which the device collects and stores said data.
2. Description of the Background
Electronic Surveillance (“ES”) systems are used on all modern United States (U.S.) Navy ships. These systems receive RF signatures in the form of pulse data and digitize them. The data is then processed in order to identify signals and determine the nature of the signals, threatening or non-threatening, for the purpose of theater awareness and self-defense. The data processing is typically accomplished by sending the data through a presorter, filtering it, and comparing the filtered data to stored sets of parameters. Monitoring the performance of processors within ES systems currently in use on U.S. Navy ships is required for continued improvement in recognition capabilities.
Previously, such monitoring was accomplished by analyzing the ES system's response to controlled stimuli. The stimuli is typically supplied by radiating RF modulated pulses at the ES system antennas, injecting RF modulated pulses into the ES system cables, or using system specific built-in-test (BIT) capabilities. Each of these methods supplies RF modulated pulses that the ES system processes into digital PDWs. The ES system responds to the supplied RF pulses by either displaying the correct threat identification or producing active transmissions based upon a correct threat identification. Recordings are made of the response. By analyzing the recordings a judgment can be made on how well the system works.
Unfortunately, due to the ever-increasing complexity and density of emissions in the RF spectrum this method of assessing ES system performance is out-dated and insufficient. Specifically, it does not allow for a more detailed analysis, based upon a realistic and comprehensive RF environment, to determine the cause of an incorrect response. Adequate assessment of the performance capabilities of a particular ES system requires an in-depth analysis of all received (vice supplied) RF pulse activity for a given time period. Only with such an assessment can there be a realistic improvement in the development of radar and threat recognition algorithms.
Many ES systems and electronic counter measure (ECM) systems have the ability to sample and temporarily store the RF parameter data of a singular received RF pulse. This pulse is finely sampled across its duration. This sampling information allows the recreation of the pulse for output. However, modern ES and ECM systems do not possess long-term multi-pulse storage capability. In ECM systems the goal of the memory is to affect a short delay in the retransmission of data. This delay equates to range when viewed from a hostile perspective. Digital radio frequency memory (DRFM) or other memory is used to capture, store and then retransmit RF energy a short time later. This is often referred to as an RF delay line. Once the data has been re-transmitted, it is no longer held in memory. For example, U.S. Pat. Nos. 4,891,646, 4,713,662 and 4,743,905 to Wiegand, U.S. Pat. No. 4,885,587 to Wiegand et al., and U.S. Pat. No. 4,928,104 to Schaffer all discuss various forms of DRFM for use within ECM systems. Specifically, these DRFMs are designed for use within active radar jamming systems. In each form the purpose of the DRFM is to allow the radar jamming system to capture received radar signals, manipulate or alter them in time or phase, as necessary, and return them on demand to confuse enemy radar systems. U.S. Pat. No. 5,032,839 to Even-Or employs optical RF memory for the same purpose.
Several other prior art references also disclose the use of short-term memory to improve the speed and accuracy of ECM or ES systems.
U.S. Pat. No. 4,145,691 to Freeling et al. patents a memory system which finds particular use in ECM systems. It uses memory to establish a feedback loop to recirculate RF burst signals which are emitted by enemy radar systems.
U.S. Pat. No. 4,217,580 to Lowenschuss discloses a complete ECM system. In this system RF signals are converted to digital words. The digital words are then pre-sorted. Once a predetermined number of digital words associated with one radio frequency signal is collected, that data is passed to a computer. This computer will then compare the signature to that of a library, recognize the threat and determine the counter technique called jamming. U.S. Pat. No. 4,879,561 to Inkol discloses a filter system for analyzing interleaved pulse descriptor words (PDW) received from a multiplicity of radar signals. This system incorporates a buffer memory. The buffer memory is organized to allow data corresponding to a particular radar emitter to be efficiently accessed for further analysis within the radar system.
U.S. Pat. No. 4,025,920 to Reitboeck et al. discloses an apparatus and method for identifying incoming radar signals by comparing them with stored sets of parameters. Similarly, a radio frequency detection and collection system (RFD/CS) produced by Wide Band Systems, Inc. uses an antenna array and instantaneous frequency measurement (IFM) receivers to collect RF signals and convert them into PDWs. The PDWs are then transmitted to a computer workstation for analysis. The purpose of the computer workstation in this RFD/CS system is used to compare the incoming PDWs with stored parameters in order to identify the intercepted emissions. None of the above-mentioned references discloses a system that records the total RF environment for long-term use.
Thus, there is a need for a portable PDW collector designed to passively collect and record all received RF emissions for later comparative analysis in a laboratory environment. This portable PDW collector enables the capture for analysis of all RF activity within any given theater of operation or important point around the world. Such a PDW collector would provide a convenient and cost-effective device that can easily be carried onboard a U.S. Navy vessel and integrated into its ES system. The alternatives to this solution, including installation on each vessel of another independent ES system capable of collecting the required data or an invasive redesign of all ES systems, are cost prohibitive.